1. Field of the Invention
The present invention relates generally to methods for controlling the freezing capacity of freezing AC ice-water systems, and more particularly, to a method for controlling the freezing capacity of a fixed-frequency freezing AC ice-water system.
2. Description of Related Art
Generally, requirement ends in business places or office buildings for temperature control (e.g. air conditioners, central air conditioning systems, freezers, refrigerators etc.) require large power output to achieve a sufficient cooling effect. Several requirement ends in a business place are usually connected to a rear end chiller and exchange heat with the chiller for achieving desired cooling effects. For example, freezers and refrigerators in a supermarket or a warehouse are connected to a rear end chiller so as to allow heat exchange to occur therebetween through a cooling fluid provided by the chiller, thereby achieving freezing and refrigerating effects.
In practice, a chiller usually supplies a huge freezing capacity, which thus results in high electric power consumption. For example, a chiller in a supermarket supplies several tons to several hundreds of tons of freezing capacity, thereby resulting in high electric power consumption and high cost. If the freezing capacity during startup of the chiller can be effectively utilized and the number of startup and shutdown events can be reduced, the freezing cost can be greatly reduced.
Accordingly, a fixed-frequency chiller with a plurality of compressors is developed, wherein the number of operating compressors varies with the total supply of freezing capacity so as to reduce electric power consumption and save cost. It is because that the supply of freezing capacity of the fixed-frequency chiller is positively proportional to the number of operating compressors, and each of the operating compressors operates at full speed once it starts up. That is, each of the compressors of the fixed-frequency chiller is completely started up (as shown at point A of FIG. 1) or completely shut down (as shown at point B of FIG. 1). FIG. 1 is a plot showing the relationship between the electric power consumption and freezing capacity supply of a typical fixed-frequency chiller. When one of the compressors of the fixed-frequency chiller starts to operate, it operates at the maximum freezing capacity and has an electric power consumption of 100% of the rated power. By increasing the number of operating compressors according to the required total supply of freezing capacity, the fixed-frequency chiller achieves an operating effect similar to that of a variable-frequency chiller. However, along with continuing global warming, only using such a fixed-frequency chiller with the number of operating compressors varied according to the required total supply of frequency capacity cannot meet the high demand for carbon emission reduction.
Therefore, it is imperative to provide a method for controlling the freezing capacity of a fixed-frequency freezing AC ice-water system so as to overcome the above-described drawbacks.